Many electric locomotives derive power from an overhead contact wire system (commonly known as an overhead contact line or OCL). Such systems typically comprise one or more pantograph mechanisms that are placed on the roof of a locomotive. Each pantograph mechanism comprises a current collector that abuts against the OCL in use and enables current to be drawn from the overhead wire for driving the locomotive, and a mechanism for raising or lowering the current collector relative to the locomotive. Such current collectors typically comprise a block of conducting material (typically, carbon) that abuts against the OCL in use and a carrier on which the block is mounted—the carrier being coupled to the aforementioned mechanism.
In typical pantograph mechanisms the collector is forced against the OCL by the aforementioned raising/lowering mechanism. The force with which the collector is held against the OCL is important in that too much force increases the rate at which the collector wears, increases the operating temperature of the collector block and increases the risk of damage to the collector and OCL, whereas too little force can cause arcing between the OCL and the collector—which arcing may damage the collector and/or OCL and cause excessive noise.
As will be appreciated, any damage caused to the OCL has a negative effect on both track and train operators, and it is often the case that the company responsible for damaging the OCL is charged a penalty for preventing other company's scheduled operation of train or track. Similarly, accelerated wear of collectors or damage thereto inevitably increases maintenance costs for the train operators.
It would be advantageous, therefore, to monitor the strain and temperature of a collector as it is forced against and moved along an OCL, and one such system that purports to provide this functionality is disclosed in UK Patent No. 2408570.
This UK patent discloses a monitoring system that employs a series of optical Fibre Bragg Grating (FBG) sensors (the like of which are well known in the art) to monitor the strain experienced by the collector and the temperature of the collector as the collector abuts against and moves along an OCL.
In the preferred arrangement described in the example set out in detail on pages 10 to 12 of this UK patent, it is disclosed that the optimum position for mounting FBG strain sensors is at the base of the carrier for the conducting block, and that the optimum position for mounting FBG temperature sensors is at the interface between the block and the carrier. The patent further discloses that a collector was developed which had three sensor pads fitted for strain measurement, each said pad including a strain FBG and a compensating FBG temperature sensor. Each of the pads was adhered to the base of the carrier with the strain sensor in contact with the carrier. The carrier was then bonded to a carbon block that included an embedded FBG temperature sensor. The resulting collector configuration is shown in cross-section in FIG. 2b of the UK patent.
The arrangement described in this patent was developed as part of a Fifth Framework Programme project (Project Reference: G3RD-CT-2002-00812) known as “CATIEMON”, and although the aforementioned patent asserts that the collector described therein provided a means for permanently monitoring the thermal and mechanical strain load caused by a train with a pantograph running under an OCL, it is actually the case that the CATIEMON project from which the collector described in the UK patent emerged was declared to be a failure and the mooted monitoring system was not implemented. The principal reason for this was that the monitoring system developed under the auspices of the project (as described in the patent) did not in fact function as expected, and did not reliably enable the strain and temperature of a collector to be accurately monitored.
The present invention seeks to address these problems and in one aspect to provide a monitoring system that can accurately and reliably measure the strain and temperature of a current collector.